Recently, an optical fiber transmission system that compensates for crosstalk between spatial modes using multi-input and multi-output (MIMO) signal processing technology and performs space-division multiplex transmission is developed. As an example of transmission media applicable to the optical fiber transmission system, an MCF with a coupled-core group in which a plurality of cores are arranged such that mode coupling is generated is known. The coupled-core group can be regarded as one multi-mode transmission path substantially by generating the mode coupling between the plurality of cores.